From 281 & 1604: Take 281 South and heat east onto Loop 410.  Take the I-35 South ramp and Exit Walzem.  Turn left under I-35 and Rackspace Hosting will be on your right.

From 35 North: Take I-35 South toward San Antonio and exit Walzem. Turn left under I-35 and Rackspace Hosting will be on your right.

From IH-10 & 1604:  Take IH-10 East (toward San Antonio.  Take the 35-North exit.  Exit Walzem and take a right.  Rackspace will be on your right.

From I-37 & Loop 410:  Take I-37 North (it will become 281 N).  Take the I-35 North ramp.  Exit Walzem and take a right.  Rackspace will be on your right.